The present invention relates to a novel class of organopolysiloxanes and a composition curable at room temperature containing the same.
In the prior art, several types of room temperature curable organopolysiloxane compositions are known which are storable over a long period of time under a hermetically sealed condition but curable when exposed to atmospheric air even at room temperature by reacting with atmospheric moisture to be converted into a rubbery elastomer. These room temperature curable organopolysiloxane compositions are classified into so-called two-package type ones and one-package type ones. The compositions of the former type are relatively unstable even in a sealed condition when all of the components have been blended together so that the composition is prepared in two packages each containing different components and the contents of the two packages are blended together directly before use to initiate the curing reaction as a sealing material, adhesive agent and the like.
On the other hand, the compositions of the latter type are sufficiently stable even when all of the components are blended together provided that exclusion of the atmospheric moisture is complete. Naturally, these one-package type compositions are preferred in most of applications to the two-package type ones by virtue of the convenience in their use.
One-package type room temperature curable organopolysiloxane compositions are cured on exposure to atmospheric air by the mechanism of a condensation reaction between functional groups bonded to the silicon atoms in the organopolysiloxane molecules. Therefore, the one-package type room temperature curable organopolysiloxane compositions are further classified according to the types of the condensation reaction or, in particular, according to the combination of the functional groups from which various kinds of condensation products are formed by the condensation reaction.
For example, conventional compositions of the type emit carboxylic acids such as acetic acid, amines, oximes or alcohols as the condensation product and they are called de-carboxylic acid type, deamination type, deoximation type and dealcoholation type ones, respectively. These compositions have, of course, their own advantages and disadvantages.
It is readily understood that the carboxylic acids, amines and oximes emitted from the respective compositions in the curing thereof are toxic or corrosive so that their use must be carried out under sufficient ventilation to avoid the problem of workers' health. In addition, their use on or in the vicinity of metal parts is not recommended due to the rusting by the corrosive condensation products even with an anticorrosion treatment by use of a primer or undercoating.
The dealcoholation type compositions are, on the other hand, free from the problem of corrosion or toxicity since an alcohol as the condensation product is non-corrosive and may be non-toxic as in ethyl alcohol. The dealcoholation type compositions are, however, defective in different ways that the storability of the composition is relatively poor, the curing velocity at room temperature is low taking unduly long time for complete curing, especially, when the layer of the composition to be cured is thick and the mechanical properties of the cured products thereof are inferior with brittleness.
Further, there has been proposed a room temperature curable organopolysiloxane composition curable by the mechanism in which a ketone is formed as the condensation product in the crosslinking reaction with the atmospheric moisture (see, for example, Japanese Patent Publication 42-23567). The curable compositions of this type are free from the problems of corrosion or toxicity but are defective in the lack of adhesivity on the surface of metals or plastics.